1. Field of the Invention
The present invention relates to a steam turbine and a turbine rotor, more particularly, to a steam turbine and a turbine rotor allowing the use of high-temperature steam at 620° C. or higher.
2. Description of the Related Art
For most of high-temperature parts in thermal power generation facilities, ferritic heat resistant steels excellent in manufacturing performance and economic efficiency have been used. A steam turbine of such a conventional thermal power generation facility is generally under a steam temperature condition on order of not higher than 600° C., and therefore, its major components such as a turbine rotor and moving blades are made of ferritic heat resistant steel.
However, in recent years, improvement in efficiency of thermal power generation facilities have been actively promoted from a viewpoint of environmental protection, and steam turbines utilizing high-temperature steam at about 600° C. are operated. Such a steam turbine includes components requiring characteristics that cannot be satisfied by characteristics of the ferritic heat resistant steel, and therefore, these components are sometimes made of a heat resistant alloy or austenitic heat resistant steel more excellent in high-temperature resistance.
For example, JP-A 7-247806 (KOKAI), JP-A 2000-282808 (KOKAI), and Japanese Patent No. 3095745 describe arts to construct a steam turbine power generation facility with the minimum use of an austenitic material for a steam turbine utilizing high-temperature steam at 650° C. or higher. For example, in the steam turbine power generation facility described in JP-A 2000-282808 (KOKAI), a superhigh-pressure turbine, a high-pressure turbine, an intermediate-pressure turbine, a low-pressure turbine, a second low-pressure turbine, and a generator are uniaxially connected, and the super high-pressure turbine and the high-pressure turbine are assembled in the same outer casing and thus are independent from the others.
Further, in view of global environmental protection, a need for higher efficiency enabling a reduction in emissions of CO2, SOx, and NOx is currently increasing. One of the most effective plans to enhance plant thermal efficiency in a thermal power generation facility is to increase steam temperature, and the development of a steam turbine on order of 700° C. is under consideration.
Further, for example, JP-A 2004-353603 (KOKAI) describes an art to cool turbine components by cooling steam in order to cope with the aforesaid increase in the steam temperature.
In the development of the aforesaid steam turbine on order of 700° C., how strength of, in particular, turbine components can be ensured is currently groped for. In thermal power generation facilities, improved heat resistant steel has been conventionally used for turbine components such as a turbine rotor, nozzles, moving blades, a nozzle box (steam chamber), and a steam supply pipe included in a steam turbine, but when the temperature of reheated steam becomes 700° C. or higher, it is difficult to maintain high level of strength guarantee of the turbine components.
Under such circumstances, there is a demand for realizing a new art that is capable of maintaining high level of strength guarantee of turbine components even when conventional improved heat resistant steel is used as it is for the turbine components in a steam turbine. One prospective art to realize this is to use cooling steam for cooling the aforesaid turbine components. However, to cool a turbine rotor and a casing by the cooling steam in order to use the conventional material for portions, for instance, corresponding to and after a first-stage turbine, a required amount of the cooling steam amounts to several % of an amount of main steam. Moreover, since the cooling steam flows into a channel portion, there arises a problem of deterioration in internal efficiency of a turbine itself in accordance with deterioration in blade cascade performance.